Field of the Invention
The present invention relates to a sheet conveying apparatus and an image forming apparatus, and more particularly, to the configuration of a sensor that detects a sheet passing through a curved sheet conveyance path.
Description of the Related Art
In recent years, there has been a demand for high speed and high accuracy of an image forming operation and an image reading operation in image forming apparatuses such as copying machines, printers, or facsimiles and image reading apparatuses such as scanners. Accordingly, there is a demand for high speed and high accuracy in sheet conveying apparatuses that are installed in the image forming apparatuses and the image reading apparatuses and convey a sheet such as a recording medium or a document.
The related sheet conveying apparatuses include a sheet conveyance path through which a sheet passes and a number of sensors detecting that the sheet passes is installed along the sheet conveyance path. As the sensors, transmissive optical sensors have been used which include a light source irradiating a sheet with light, light-receiving elements arranged in the light source, and a prism disposed at a position facing the light-receiving elements (see Japanese Patent Laid-Open No. 2003-040490).
In the transmissive sensors, the light-receiving elements detect light reflected from the prism when no sheet is present between the prism and the light-receiving elements. However, the light-receiving elements do not detect the light because the light is blocked when a sheet is present. Therefore, it is possible to detect whether a sheet is present depending on whether the light-receiving elements detect the light reflected from the prism. However, the transmissive sensors, which utilize the configuration in which the sheet blocks the light, may not detect the sheet in a case where the sheet is a sheet such as an OHP sheet through which the light passes.
On the other hand, as other optical sensors, there are reflective sensors which include a light source and light-receiving elements arranged in the light source and in which the light source irradiates a sheet passing through a sheet conveyance path with light and the light-receiving elements receive the light arriving at and reflected from the sheet. The irradiation light is regularly reflected from an OHP sheet or the like. Accordingly, with the above-configured reflective sensors, the OHP sheet or the like which may not be detected with the transmissive sensors can be detected.
However, some related sheet conveying apparatuses include a curved sheet conveyance path. When a transmissive sensor is disposed along such a curved sheet conveyance path and a sheet passes through the sheet conveyance path, the sheet is conveyed in a state where the sheet is angled with respect to the irradiation light from the light source. Here, in the case of the reflective sensors, the irradiation light does not vertically arrive at the conveyed sheet. Therefore, particularly, in a sheet such as the OHP sheet for which irregular reflection is small, the light-receiving element may rarely detect the light reflected from the sheet, as illustrated in FIG. 2B described below.
Accordingly, to easily detect the OHP sheet that has been angled with respect to the light, for example, it is necessary to diffuse the irradiation light or increase the illuminance. However, when the irradiation light is diffused or the illuminance is increased, the light does not arrive at the sheet but a passage member forming the sheet conveyance path so as to be reflected from the passage member. Therefore, there is a concern that the light-receiving element may detect the reflected light so as to cause erroneous detection.
Accordingly, to prevent such erroneous detection, that is, to reliably detect the sheet, for example, it is necessary to provide an escape hole in a portion of the passage member at which the diffused light arrives. However, if the escape hole is provided, there is a concern that a sheet may be jammed in the escape hole at the time of conveying the sheet at high speed.
Accordingly, the invention is devised in the light of the above-mentioned circumstance and is directed to provide a sheet conveying apparatus and an image forming apparatus capable of reliably detecting a sheet being conveyed at high speed along a curved sheet conveyance path.